1. Field of the Invention
This invention relates to automobile wheel alignment and more particularly relates to a method and apparatus of using electronic angle measuring equipment for determining the actual toe of rear and front vehicle wheels relative to the longitudinal axis of the vehicle and for indicating the corrections needed for achieving the proper toe of each wheel.
2. Description of the Prior Art
Reference is made to Lill U.S. application Ser. No. 261,445 filed May 8, 1981, now continuation application Ser. No. 540,911 filed on Oct. 12, 1983. A portion of the preferred alignment head used in performing the method herein is disclosed in Ragan U.S. application Ser. No. 261,441 which was also filed on May 8, 1981, now U.S. Pat. No. 4,408,879 which issued on Oct. 11, 1983. These applications are presently assigned to the assignee of the present invention.
Electro-optical methods and apparatus are known for determining and correcting the toe of front and/or rear wheels of a vehicle. However, when correcting the toe of rear wheels the operator is required to re-aim the line of sight after each adjustment of the rear wheels when using prior art systems thereby making the rear wheel toe alignment procedure time consuming and requiring the operator to use different alignment techniques for front and rear toe corrections. Copending Lill continuation U.S. application Ser. No. 540,911 discloses such a prior art method and apparatus and provides a pair of visual image aiming systems in the aligner heads rather than a pair of light beam projector aiming systems, which light beam projectors are the preferred embodiment used in the practice of the method of the present invention. Furthermore, the method disclosed in the Lill application does not include an electronic memory which individually stores to toe angle of one non-steerable wheel at a time while the toe of the other wheel is being corrected by an operator who observes a running display of the toe angle as corrections are being made thereby making readjustments of the line of sight unnecessary.
Ragan U.S. application Ser. No. 261,441, now U.S. Pat. No. 4,408,879 discloses a beam projector, two of which are used to project light beams longitudinally of the vehicle and are the preferred optical alignment heads used in performing the method of the present invention. Each Ragan type projector used herein also includes cross toe beam projectors and cooperating sensors of the type disclosed in U.S. Pat. No. 4,180,326 which issued to Chang on Dec. 25, 1979 and is assigned to the assignee of the present invention.
The preferred structure for mounting the alignment heads on the associated vehicle wheels is disclosed in assignee's Ragan U.S. Pat. No. 4,285,136 which issued on Aug. 25, 1981. This patent discloses a bracket which mounts the optical alignment head on a wheel so that the head will hang from the associated bracket with its longitudinal axis substantially horizontal and parallel to the plane of rotation of the wheel.
The following U.S. patents are also pertinent to the present invention:
______________________________________ 4,097,157 Lill June 27, 1978 4,130,362 Lill et al December 19, 1978 4,150,897 Roberts, Jr et al April 24, 1979 4,154,531 Roberts, Jr et al May 15, 1979 ______________________________________
All of the above applications and patents are presently assigned to the assignee of the present invention and disclose prior art wheel alignment mechanisms. The disclosures of these applications and patents are incorporated by reference herein.
Other four wheel toe alignment methods and apparatus are known wherein four alignment heads, one for each wheel, must be used for obtaining readings relating to rear wheel toe. The method requires extra steps to read the position and direction of the rear wheel. For example, a mechanical change is necessary to change mirrors to targets on the rear wheels during alignment, and certain electronic controls must be actuated on the front heads or on the console when performing functions relating to the rear wheels. The four head method is also subject to accumulated errors when determining rear toe since the residual error of runout of all four wheels; and the angle reading error between the right rear wheel and right front wheel, the right front wheel and the left front wheel and the left front wheel and left rear wheel, are all incorporated when determining the corrections needed to provide the proper toe of the rear wheels.